1. Field of the Invention
The embodiments of the invention relate to a liquid crystal display device, and more particularly, to a slim-sized liquid crystal display device and a liquid crystal display device that maintains balance of a driving signal supplied to lamps in an accompanying light source.
2. Discussion of the Related Art
Generally, liquid crystal display devices are widely used due to advantageous characteristics of light weight, thin profile, and low power consumption. As a result, liquid crystal display devices are widely used in office automation equipment and audio/video equipment.
A liquid crystal display device includes a plurality of control switches arranged in a matrix and controls the amount of light being transmitted in accordance with a signal applied to the control switches, thereby generating a desired image. Because the liquid crystal display device is not a self luminous display device, it requires a separate light source, such as a backlight unit.
A backlight unit may be generally classified as a direct type and an edge type in accordance with the location of a light source. The edge type backlight unit has a light source along one side of a liquid crystal display device, and irradiates light from the light source to a liquid crystal display panel through a light guide plate and a plurality of optical sheets. The direct type backlight unit has a plurality of light sources disposed directly under a liquid crystal display panel, and irradiates light from the light sources to the liquid crystal display panel through a diffusion plate and a plurality of optical sheets. Recently, the direct type backlight unit is more often used in LCD TVs because it has improved brightness, more consistent light uniformity and better color purity, as compared to the edge type backlight.
A cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”) and an external electrode fluorescent lamp (hereinafter, referred to as “EEFL”) may be used for a light source in a backlight unit. To drive the lamps, a power transmission control device called an inverter is utilized. The inverter is electrically connected to the lamps of the backlight unit and serves to amplify a voltage and to control a current so that a high voltage and an appropriate current can be delivered to the lamps.
FIGS. 1a and 1b are views showing a two-board inverter according to the related art. As shown in FIGS. 1a to 1b, an inverter 12 is mechanically mounted to opposite sides of a back surface of a bottom cover 10. The bottom cover 10 accommodates lamps 14 and supplies a driving power to the lamps 14 through a lamp wire 18. A high-capacity transformer 16 and a plurality of passive devices (not shown) are mounted on a printed circuit board (hereinafter, referred to as “PCB”) of the inverter 12. The transformer 16 is a means for raising/reducing an input voltage by the turn ratio of primary coil and secondary coil that are wound around an iron core, and occupies a relatively large volume compared to the other passive devices. In particular, the inverter 12 and the PCB are arranged perpendicularly to the lengthwise dimension of the lamps 14. Also, the inverter 12 projects from the back surface of the bottom cover 10 to the mounting height of the transformer 16, which acts as a limitation in realizing a slim liquid crystal display device. Further, because the inverter 12 is arranged at both sides of the back surface of the bottom cover 10 (two-board inverter), space for a mountable space of a system module, such as a digital board or power board, is restricted and reduced.
FIGS. 2a and 2b are views showing a one-board inverter according to the related art. To increase the mountable space of the system module, a one-board inverter method has been proposed as shown in FIGS. 2a and 2b. In FIGS. 2a and 2b, an inverter 22 is mechanically mounted to a lateral side of the back surface of a bottom cover 20. The bottom cover 20 accommodates lamps 24 and supplies a driving power to the lamps 24 through a lamp wire 28. A high-capacity transformer 26 and a plurality of passive devices (not shown) are mounted on a printed circuit board (hereinafter, referred to as “PCB”) of the inverter 22. In particular, the inverter 22 and the PCB are arranged perpendicular to the lengthwise dimension of the lamps 24. The one-board inverter method has a fatal disadvantage in that because the inverter 22 is arranged further toward either one side from both electrodes of the lamps 24, left and right balance of a driving current delivered to the lamps 24 is lacking. Further, this method has another limitation in realizing a slim liquid crystal display device because the inverter 22 still projects from the back surface of the bottom cover 20 to the mounting height of the transformer 26.
Moreover, when the inverter according to the related art projects from the back surface of the bottom cover, the possibility that an electromagnetic interference may occur between the inverter and the system module increases. Furthermore, because the inverter according to the related art is arranged adjacent to the electrodes of the lamps, heat generation of the inverter is increased by the lamp heat, thereby decreasing inverter efficiency.